From crack-prone to crack-free: Unravelling the roles of LaB6 in a ß-solidifying TiAl alloy fabricated with laser additive manufacturing

The 4th generation of intermetallic.-TiAl based alloy, the so-called ss-solidifying TiAl, has attracted great attentions due to its promising high-temperature properties. But it is intrinsically brittle and crack-prone, which lowers the processability of laser additive manufacturing (LAM) that offers an effective pathway for material processing and design. Thus, improving the mechanical properties, particularly the room temperature plasticity, of LAMed ss-solidifying TiAl alloy is of technical interest and theoretical importance. Based on previous results, the present work investigates the synergistic roles of La and B in grain refinement and crack elimination in a LAMed ss-solidifying TiAl alloy with LaB6 addition (0-2 wt%). Results show that La2O3 and TiB in-situ formed via reaction between the ss-solidifying TiAl and the added LaB6 nanoparticles. Microstructural feature, phase transformation texture and mechanical properties at both room and high temperatures can be optimized through controlling the LaB6 addition level. 0.5 wt% LaB6 has been determined as the optimized addition, at which the balanced mechanical properties at both room temperature and 800 degrees C can be achieved for the LAMed ss-solidifying TiAl alloy. Excessive LaB6 addition led to agglomeration of in-situ formed precipitates, reducing density and therefore deteriorating mechanical properties. The study offers an in-depth understanding of the effective grain refining approach to overcome the intrinsic brittle nature of ss-solidifying TiAl through optimized doping of LaB6.

Automated summary

This study investigates the synergistic roles of La and B in grain refinement and crack elimination in a LAMed ss-solidifying TiAl alloy with LaB6 addition. Results show that La2O3 and TiB in-situ formed via reaction between the ss-solidifying TiAl and the added LaB6 nanoparticles. The optimal addition level of 0.5 wt% LaB6 can achieve balanced mechanical properties at both room temperature and 800 degrees C. Excessive LaB6 addition leads to agglomeration of in-situ formed precipitates, reducing density and deteriorating mechanical properties.